The present invention relates to an electronic engine control system for controlling an engine output torque by controlling an intake air flow rate by an electronically controlled throttle valve and controlling a fuel injection amount by a fuel injector.
Conventionally, transfer of a demanded torque of a traveling system to an engine control system and reflection of the demanded torque to engine control are performed in the following manner.
For example, Japanese Patent Application Laid-Open No. Heisei 7-47862 discloses an automatic cruise control, in which a throttle command is derived from a torque command in consideration that directly using a difference (V0xe2x88x92Va) between a target vehicle speed V0 and an own vehicle speed Va multiplied by a constant is not achieve satisfactorily high accuracy and response.
On the other hand, Japanese Patent No. 2611239 proposes a method for deriving a throttle valve open degree from the target torque, induction pressure and an engine revolution speed on the basis of a physical model with pointing out that when a linear control logic is applied for a control object, i.e. vehicle, in which linear relationship between a control input (throttle valve open degree) and a control output (vehicle speed) is not established, control rule has to be designed per each operational range, and in case of PID control for controlling a throttle valve open degree to open and close depending upon a difference between the target vehicle speed and the actual vehicle speed is not satisfactory in control precision and response ability.
The foregoing conventional systems is partially similar to the present invention in focusing the target torque and can expect superior control precision and response ability in comparison with PID control of speed difference.
However, while the foregoing prior arts propose to derive the throttle valve open degree from the throttle valve open degree, no consideration has been given for lean-burn. Therefore, it has not been considered a fact that the throttle valve open degree should be different at the same target torque between a combustion condition at stoichiometric air/fuel (A/F) mixture ratio and a combustion condition at lean mixture. For instance, A/F mixture ratio is 14.7 at stoichiometric condition and A/F mixture ratio is 40 at lean-burn condition. Therefore, there is 2.7 times of difference in air equivalent to require greater difference in the throttle valve open degree.
In addition, Japanese Patent Application Laid-Open No. Heisei 7-47862 does not discuss about a particular method for establishing relationship between the torque and the throttle valve open degree. Also. Japanese Patent No. 2611239 fails to disclose particular functions.
It is therefore an object of the present invention to provide a control system for an automotive vehicle which can realize superior control precision and response ability by an intake air flow rate control on the basis of a fuel injection amount which is, in turn, derived on the basis of a target torque or a target load signal even in lean-burn condition.
In order to accomplish the above-mentioned and other objects and in accordance with the first aspect of the invention, a control system for an automotive vehicle comprises: control means for controlling at least one of vehicle speed, a vehicular distance, driving wheel speed, slip ratio toward a target value; means for deriving a target torque of an engine on the basis of the target value; vehicle condition control means having means for deriving a fuel injection amount for the engine on the basis of the target torque of the engine; means for deriving a target air supply amount to the engine on the basis of the fuel injection amount derived by the vehicle condition control means; means for deriving an actual air supply amount of the engine; and means for controlling the detected actual air supply amount toward the target air supply amount.
In the alternative, in accordance with the second aspect of the present invention, a control system for an automotive vehicle comprises control means for controlling at least one of vehicle speed, a vehicular distance, driving wheel speed, slip ratio toward a target value; means for deriving a target torque of an engine on the basis of the target value; vehicle condition control means having means for converting the target torque of the engine to a reference fuel injection amount (Tp2); means for deriving an air amount corresponding to a target fuel injection amount (Tp3) of the engine derived on the basis of a target air/fuel ratio determined depending upon the reference fuel injection amount (TP2) and operating condition of the vehicle; means for deriving an air amount corresponding the basic fuel injection amount Tp1 of the engine at the stoichiometric air/fuel ration (A/F=14.7) on the basis of an intake air flow rate of the engine and an engine revolution speed; and means for controlling a throttle valve open degree for controlling the air amount corresponding to the basic fuel injection amount (Tp1) toward the air amount corresponding to the target fuel injection amount (Tp3).
In the preferred construction, converting means for converting the target torque into the reference fuel injection amount (Tp2) of the engine performs conversion with one of a function, a table and a map indicative of the target torque and the reference fuel injection amount (Tp2).
The control system may further comprise means for deriving the reference fuel injection amount (Tp2) on the basis of a torque corresponding to an acceleration depression magnitude in addition to the means for deriving the reference duel injection amount (Tp2) derived by conversion from the target torque, and reference fuel injection amount selecting means for selecting one of the reference fuel injection amount (Tp2) depending upon operational demand of a driver. In such case, the means for deriving the reference fuel injection amount (Tp2 on the basis of the torque corresponding to the accelerator depression magnitude includes means for converting the reference fuel injection amount (Tp2) based on the accelerator depression magnitude into the torque using an inverse function of converting means for converting from the target torque into the reference fuel injection amount (Tp2) and a reverse retrieval of the table or map.
The control may be performed using at least one of control parameters among air/fuel ratio, spark ignition timing, fuel injection start timing, fuel injection termination timing, EGR ratio, control parameter of swirl flow in an engine cylinder in addition to control of the throttle valve open degree upon controlling the air amount corresponding to the basic fuel injection amount (Tp1) to the air amount corresponding to the target fuel injection amount (Tp3). In such case, the control parameters may include three kinds for stoichiometric mixture combustion, homogenous lean combustion and stratified lean combustion depending upon operating condition of the engine.
The vehicle condition control means may include automatic cruise control means for controlling a traveling speed of the automotive vehicle constant, vehicular distance control means for controlling vehicular distance to a leading vehicle, traction control means for controlling driving wheel speed of the vehicle and side slip control means, and the control system further comprises means for transmitting the target torque from the vehicle condition control means to the engine control means. The first reference fuel injection amount (Tp2) converted from the target engine torque derived by the automatic cruise control means may be used during cruising under automatic cruise control and the second reference fuel injection amount (Tp2) derived at least on the basis of an accelerator depression magnitude under inoperative state of automatic cruise control, and
even under automatic cruise control, the second reference fuel injection amount (Tp2) is retrieved on the basis of the accelerator depression magnitude on the basis of correspondence to conversion when a demanded torque of the driver is greater than the target engine torque. In the alternative, the first reference fuel injection amount (Tp2) converted from the target engine torque derived by the vehicular distance control means is used while vehicular distance control is active and the second reference fuel injection amount (Tp2) derived at least on the basis of an accelerator depression magnitude under inoperative state of vehicular distance control, and even under vehicular distance control, the second reference fuel injection amount (Tp2) is retrieved on the basis of the accelerator depression magnitude on the basis of correspondence to conversion when a brake is depressed or a demanded torque of the driver is greater than the target engine torque. In the further alternative, the first reference fuel injection amount (Tp2) converted from the target engine torque derived by the traction control means or side slip control means may be used while the traction control means or the side slip control means is active for controlling driving wheel speed or tire slip ratio and the second reference fuel injection amount (Tp2) derived at least on the basis of an accelerator depression magnitude under inoperative state of traction control or side slip control.
According to the third aspect, a control method for an automotive vehicle comprises the steps of: controlling a vehicular condition of at least one of vehicular speed, vehicular distance, driving wheel speed and slip ratio toward a target value; replacing the target value into a target torque of an engine; deriving a fuel injection amount of the engine on the basis of the target torque of the engine; deriving a target air supply amount on the basis of the fuel injection amount; deriving an actual air supply amount of the engine on the basis of detected vehicular condition; and controlling g the actual air supply amount thus derived toward the target air supply amount.
According to the fourth aspect of the invention, a control method for an automotive vehicle comprises the steps of: controlling at least one of vehicle speed, a vehicular distance, driving wheel speed, slip ratio toward a target value; deriving a target torque of an engine on the basis of the target value; converting the target torque of the engine to a reference fuel injection amount (Tp2); deriving an air amount corresponding to a target fuel injection amount (Tp3) of the engine derived on the basis of a target air/fuel ratio determined depending upon the reference fuel injection amount (TP2) and operating condition of the vehicle; deriving an air amount corresponding the basic fuel injection amount Tp1 of the engine at the stoichiometric air/fuel ration (A/F=14.7) on the basis of an intake air flow rate of the engine and an engine revolution speed; and controlling a throttle valve open degree for controlling the air amount corresponding to the basic fuel injection amount (Tp1) toward the air amount corresponding to the target fuel injection amount (Tp3).
According to the fifth aspect of the invention, a control system for an automotive vehicle comprises: vehicle condition control means for controlling a vehicular condition toward a target value, and obtaining a fuel injection amount for the engine according to a target load signal based on said target value; means for deriving a target air supply amount to said engine on the basis of said fuel injection amount derived by said vehicle condition control means, deriving an actual air supply amount of the engine; and controlling the detected actual air supply amount toward said target air supply amount.